The various embodiments described herein generally relate to detecting a hazardous condition within a structure. More particularly, the various embodiments relate to a detector and a method for detecting a hazardous condition using multiple criteria for improved reliability.
One example of a detector for detection of a hazardous condition is a fire detector. For example, EP 1376505 describes an exemplary fire detector that uses multiple criteria for improved reliability. The described fire detector includes a sensor arrangement, an electronic evaluation system and a housing which surrounds the sensor arrangement. Openings provide access for air and, when applicable, smoke to the sensor arrangement. The fire detector accommodates detection modules having sensors for different fire parameters, for example, an electro-optical sensor for detecting scattered light generated by smoke present in the ambient air, or one or more temperature sensors for detecting heat generated by a fire, or a gas sensor for detecting combustion gases, or combinations of these sensors.
EP 729123 describes a multiple sensor detection system. A fire detector detects a hazardous condition, such as fire, gas, or overheat, and an environmental condition detector detects another condition, such as humidity, ambient pollution level, presence or absence of sunlight. The two detectors are coupled to circuitry so that the output from the fire detector triggers an alarm condition only in the absence of an output from the environmental condition detector. That is, in the presence of a selected environmental condition (e.g., humidity or pollution), any output from the fire detector indicative of gas, fire, temperature or the like is inhibited at least for a predetermined period of time. In the absence of an output from the environmental condition detector, the fire detector produces a signal indicative of the sensed gas, temperature or fire condition.
The fire detector and detection system described above strive to minimize false alarms. However, false alarms of systems that detect and warn of hazardous conditions, such as a fire, remain a major issue in various applications and particularly those where extreme environmental conditions can lead to the formation of deceptive phenomena such as dust suspended in the air, fog, condensation or water steam. These extreme conditions may occur in transportation applications such as in aircrafts, trains, seagoing vessels, or military vehicles, satellites, building applications such as in kitchens, machine rooms or hotel rooms, or on industrial sites. The relatively high rate of false alarms arising under these extreme conditions using current detection technologies has a significant cost impact. Further, false alarms are a severe safety concern because people lose more and more confidence in fire detection systems.